Update vagrant bootstrap helpers
Update vagrant bootstrap helpers

to reference Stanford branches.
We hadn't used these previously, but they make the onboarding just a
little bit easier..

```sh
mkdir devstack
cd devstack
curl -fOL# https://raw.githubusercontent.com/Stanford-Online/configuration/master/util/install/install_stack.sh
bash install_stack.sh devstack master
```

Stanford-Online/configuration,Stanford-Online/configuration,Stanford-Online/configuration,Stanford-Online/configuration,Stanford-Online/configuration